Ring or radial

[Farmelectrics]

Just done some small alterations to a training room it's a 4mm radial in dado trunking that was already there there is 7 pcs to be plugged into circuit I suggested making it into a ring but the engineer were working for says its ok I thought all pcs had to be on ring du to high integratity earthing

 

[KAS1]

I think there's a drawing in the OSG that should explain

 

[Farmelectrics]

Kas I've seen it not recently but sure all sockets for pcs need high integrity earthing

 

[KAS1]

BS7671 in there somewhere, you're correct but I don't think they have to be on a ring, 2 cpc's though (ringed as they say) one of which can be conduit

 

[Farmelectrics]

Ok Kas so if I or should I say we run a 4mm earth back to db connected in separate earths of course this would solve the issue just for the record though what spark would disconnect an earth of a live circuit any way and be on the end of the earh leakage from the pcs always baffled me this one

 

[Sintra]

This little pdf should explain the lot.

https://www.dropbox.com/s/lyekd609rxsmo78/High integrity .pdf

 

[Richard Burns]

Computers can generate leakage currents that can cause RCD tripping problems as they can also have functional earthing requirements that suppress noise on the computer supply.
If the leakage current is high, say with ten or more computers, then the cpc should be doubled and, for a radial run, in a ring, but the live conductors do not need to be in a ring, it is only to ensure that the cpc connection is not broken by accident (i.e. high integrity earthing).
The cpcs should also be terminate in the accessories separately.

 

[KAS1]

I didn't write the regs lol, personally I'd of put them on a ring, I've worked on contracts where they've specced 4mm rings as standard so I'd of gone with your suggestion for the sake of a bit a cable and you would of then achieved the high integrity earthing as well, but I can see no reg where computers have to be on a ring, it could be a radial with 2 cpc's with one being a conduit or trunking.

 

[Farmelectrics]

Thanks for the replays guys

 

[pete555]

radial ok high integrity earth needs to be installed as a ring

 

[GLENNSPARK]

Kas I've seen it not recently but sure all sockets for pcs need high integrity earthing

then make the high integrity earth a ring by all means....

 

[telectrix]

all you need to do is use both earth tags on each socket, then from the last socket on the radial, take a 4.0mm single g/y back to DB. terminate in a different hole.

 

[Farmelectrics]

Will do tel but if you didn't what problems could this cause and how would you ever come into contact with this earth leakage as you wouldn't disconnect the earths at the db nosing the circuit was live your thoughts please

 

[telectrix]

no problems with a radial only, the ringing of the cpc is belt and braces in case of a cpc snapping off at a terminal. you can measure the earth leakage with a clamp meter if you need to, a pc has a typical leakage of around 3mA.

 

[Farmelectrics]

I no that tel but could you explain to me how you could come into contact with this earth leakage

 

[Richard Burns]

It is not coming into contact with the earth leakage that is the main problem, although that is the effect we are trying to control, it is ensuring that the piece of equipment is continuously connected to the MET.
Because the suppression filters, SM power supplies, etc., generate a potential on the earth that can deliver over 10mA there is a risk of harm to someone touching any exposed conductive parts of the equipment if the equipment is not earthed, I know a lot of the desk IT kit is double insulated now, but there is a still a reasonable amount that is not and more in server rooms.
Also the lack of an earth will render the suppression useless as the leakage current is from a functional earth and without it the transients have nowhere to go.

 

[GLENNSPARK]

It is not coming into contact with the earth leakage that is the main problem, although that is the effect we are trying to control, it is ensuring that the piece of equipment is continuously connected to the MET.
Because the suppression filters, SM power supplies, etc., generate a potential on the earth that can deliver over 10mA there is a risk of harm to someone touching any exposed conductive parts of the equipment if the equipment is not earthed, I know a lot of the desk IT kit is double insulated now, but there is a still a reasonable amount that is not and more in server rooms.
Also the lack of an earth will render the suppression useless as the leakage current is from a functional earth and without it the transients have nowhere to go.

its effectively an earth screen....dumping stray...

 

[Engineer54]

Personally i wouldn't have more than 5 PC workstations on any one circuit!! Having RCD protection on PC/IT work station circuits, is just asking to loose any unsaved data, but it still seems all too common to do so!! lol!!

High integrity earthing is specified for a purpose, and something that the OP's Engineer should have been aware of, and suggested a dual/ringing of the CPC

 

[Farmelectrics]

But in these office I'm working in there is up to 16 pcs plugged in via a dual bus track under floor

 

[itselectric]

It's not been mentioned here, but I'm almost sure from memory that the 4mm cpc has to follow the same route as the circuit cable and to be clipped with it.

 

[Engineer54]

But in these office I'm working in there is up to 16 pcs plugged in via a dual bus track under floor

So does that make it right then??